A typical hot material transfer system used to transfer preprocessed furnace feed material might consist of the following sequence:
(a) A valve on the output end of a kiln discharges the hot feed material into a transfer container below, which is mounted on a transfer car.
(b) Once the transfer container has been filled, the transfer car travels into the furnace building with the full container, which is then picked up by the furnace-charging crane. The crane raises the transfer container to an elevation just above the top of the furnace feed bins, which are located directly above the furnace.(c) The crane places the transfer container on a bin and the action of setting the container down causes it to discharge the feed material down into the bin.
The problems associated with the transportation of such hot feed materials arise from their inherent characteristics, which may include some or all of the following:
The materials are hot (up to 1000° C.), are normally abrasive and normally contain a significant amount of fines.
The hot feed materials are in a partially reduced state, and the reduction of the feed material continues as it is transferred from the kiln to the furnace feed bins. This causes a near constant but relatively benign and clean emission of CO gas. When the hot CO gas reaches air it further oxidizes to form CO2. Once the hot feed materials are exposed to air they may begin to burn (reoxidize). This reaction releases more heat and a large volume of gas. This gas is a pollutant and usually carries particulate matter.
For these reasons transfer of hot feed materials is inherently a dirty and environmentally and occupationally detrimental process. Because the hot feed material is at an elevated temperature and contains reductant ingredients, hot gases (especially carbon monoxide) are continually emitted during the transfer, sometimes with inclusion of particulate matter.
Although such emissions are released throughout the entire time the transfer container contains the feed material, these emissions are relatively small compared to those released during the filling and emptying of the container. Of these processes, by far the largest burst of dirty emissions occurs during the emptying of the transfer container. This event has the highest degree of agitation and mixing of the feed material with air. The typical hot furnace feed transfer deposits a transfer container approximately every 10 minutes. Therefore, six or more of these “bursts” occur per hour, 24 hours per day, 50 weeks per year.
There are other known means for controlling dust and pollution during the transfer of hot feed materials. One example is disclosed by U.S. Pat. No. 6,953,337 (McCaffrey et al.), which is incorporated herein by reference in its entirety. According to McCaffrey et al., an enclosed housing with a controlled atmosphere is provided between the preprocessing plant and the furnace. The feed material is preferably raised within the housing to a higher level that that at which it is discharged from the plant so that it can be fed to inclined funnel assemblies which carry the feed material to the furnace by gravity.
There remains a need for an effective and economical system for reducing or eliminating emissions during transfer of hot feed materials, and in particular from the transfer container into the feed bins.